[petsc-users] Problem with MPI, MatAXPY and SAME_NONZERO_PATTERN

[Matthew Knepley]

On Fri, Mar 27, 2015 at 9:48 AM, Klaus Kaiser <kaiser at igpm.rwth-aachen.de>
wrote:

> Hallo,
>
> I have a strange behavior in my code concerning the function MatAXPY. I
> create 3 different Matrices
>
>     ierr = MatCreateBAIJ(PETSC_COMM_WORLD, block_size, local_size,
> local_size, system_size, system_size, 0, d_nnz, 0, o_nnz,&A);
>     ierr = MatSetOption(A,MAT_NEW_NONZERO_ALLOCATION_ERR,PETSC_TRUE);
>     ierr = MatSetOption(A,MAT_KEEP_NONZERO_PATTERN,PETSC_TRUE);
>     ierr = MatSetOption(A,MAT_IGNORE_OFF_PROC_ENTRIES,PETSC_TRUE);
>
>     ierr = MatCreateBAIJ(PETSC_COMM_WORLD, block_size, local_size,
> local_size, system_size, system_size, 0, d_nnz, 0, o_nnz,&At);
>     ierr = MatSetOption(At,MAT_NEW_NONZERO_ALLOCATION_ERR,PETSC_TRUE);
>     ierr = MatSetOption(At,MAT_KEEP_NONZERO_PATTERN,PETSC_TRUE);
>     ierr = MatSetOption(At,MAT_IGNORE_OFF_PROC_ENTRIES,PETSC_TRUE);
>
>     ierr = MatCreateBAIJ(PETSC_COMM_WORLD, block_size, local_size,
> local_size, system_size, system_size, 0, d_nnz, 0, o_nnz,&Ah);
>     ierr = MatSetOption(Ah,MAT_NEW_NONZERO_ALLOCATION_ERR,PETSC_TRUE);
>     ierr = MatSetOption(Ah,MAT_KEEP_NONZERO_PATTERN,PETSC_TRUE);
>     ierr = MatSetOption(Ah,MAT_IGNORE_OFF_PROC_ENTRIES,PETSC_TRUE);
>

These creations are superfluous since you use MatDuplicate() below.


> and want to sum these three matrixes with different factors. First I fill
> the Matrix A with some values, and duplicate the structure of A to the
> other two matrices:
>
>     MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
>     MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
>     MatDuplicate(A,MAT_DO_NOT_COPY_VALUES,&Ah);
>     MatDuplicate(A,MAT_DO_NOT_COPY_VALUES,&At);
>     MatAssemblyBegin(Ah,MAT_FINAL_ASSEMBLY);
>     MatAssemblyEnd(Ah,MAT_FINAL_ASSEMBLY);
>     MatAssemblyBegin(At,MAT_FINAL_ASSEMBLY);
>     MatAssemblyEnd(At,MAT_FINAL_ASSEMBLY);
>


> After this I fill the matrices At and Ah with some other values, which are
> not beside the non zero structure (I also tried with just copying the
> Matrix A). Now after another MatAssembly


I do not understand "no beside the nonzero structure". Do you mean that the
nonzero structure is the same?

Can you first test with MAT_COPY_VALUES?


> I want to add these Matrices in the form A+c*(Ah+d*At):


>     MatAXPY(Ah,c,At,SAME_NONZERO_PATTERN);
>     MatAXPY(A,d,Ah,SAME_NONZERO_PATTERN);
>
> When I run the method with mpi and one core everything works fine.
> Starting the same method with more cores, the sum of the matrices fails. It
> seems like some values are added


Please send the full output of a failure when you use MAT_COPY_VALUES on 2
procs.

  Thanks,

     Matt


> correctly and many values are missed. Using DIFFERENT_NONZERO_STRUCTURE
> leads to the right behavior in the multi-core case, but is very slow. I
> checked with a viewer if all matrices have the same nonzero structure and
> this is the case.
>
> Does anyone know why this fails, or do I have made any wrong thoughts?
>
> I'm corrently working with a petsc version (Petsc Release Version 3.3.0,
> Patch 5, Sat Dec  1 15:10:41 CST 2012), I looked into the changelogs up to
> the current version and did not find any note about MatAXPY or MatAYPX.
>
>
> Best and Thanks a lot for your help
>
> Klaus
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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